If that is the case, then his method has very limited applications in the field. AA did not have a chance to bracket Moonrise Hernandez. In fact, he didn't even use an exposure meter, he couldn't find it!

Actually, this particular image was made more in keeping with Mortenson's methods than with his own. Since he couldn't find his exposure meter, he computed the correct exposure using the Exposure Formula and the luminance of the moon, which he wanted to be Zone VII and which he knew. (250 candles/square foot). The moon is also arguably the item of central interest in the picture. He let the chips fall where they may viz a vis the foreground shadows (which he intensified in selenium some years later). He used water bath development (D-23 if I remember correctly) which also implies development by inspection to keep from blowing the highlights in the clouds. All this is documented in Examples The Making of 40 Photographs. In any case, it's hardly a good example of the Zone System axiom that one should always 'expose for the shadows and develop for the highlights'. Unless you consider Zone VII a shadow.